As processes for producing 2,5-bis(trifluoromethyl)nitrobenzene, the following processes have been proposed.
(1) A process of nitrating 1,4-bis(trifluoromethyl)benzene by means of 100 mass % nitric acid at from 90 to 105° C. by using 24% fuming sulfuric acid as a solvent to obtain 2,5-bis(trifluoromethyl)nitrobenzene in a yield of 35% (J. Amer. Chem. Soc., 75, 4967 (1953)).
(2) A process of reacting 1,4-bis(trifluoromethyl)benzene with nitric acid for nitration in the presence of 2CF3SO3H—B(O3SCF3)3 which is formed by reaction of BCl3 and CF3SO3H in a molar ratio of 1:5, to obtain 2,5-bis(trifluoromethyl)nitrobenzene in a yield of 14% (J. Org. Chem., 60, 7348 (1995)).
(3) A process of reacting 4-chloro-3-nitrobenzotrifluoride with CF3Cu which is formed from CF2Br2 and copper, in the presence of charcoal for trifluoromethylation to obtain 2,5-bis(trifluoromethyl)nitrobenzene (Tetrahedoron Lett., 30, 2133 (1989)).
However, the above processes have the following drawbacks.
In the process (1), nitric acid is dropwise added to a mixed solution formed by dropwise adding 24% sulfuric acid to 1,4-bis(trifluoromethyl)benzene. In this process, heat is generated when the mixed acid of sulfuric acid and nitric acid is formed, and fuming sulfuric acid having a high concentration is used at a high temperature. Thus, a side reaction such as sulfonation is likely to take place, and the yield tends to be low.
In the process (2), the yield is extremely low. Further, CF3SO3H is expensive, such being disadvantageous for industrial production.
In the process (3), CF2Br2 which is expensive is used. Further, the amount of copper used is 6 times the molar quantity of 1,4-bis(trifluoromethyl)benzene, such being problematic in view of waste water disposal. Further, the process (3) is an uneconomical process, such being disadvantageous for industrial production.